Field of the Invention
The present invention relates to a zinc oxide-based transparent conductive layer having a textured surface, its manufacturing method and a transparent electrode for a solar cell using the same.
Description of the Related Art
In the case of a thin-film silicon-based solar cell, because a silicon has a small extinction coefficient, it needs to increase the efficiency of the solar cell by increasing the path of an incident light by light scattering in an absorption layer. For this purpose, the surface of a front electrode of a thin-film solar cell is textured to increase the optical conversion efficiency. Currently, the front electrode of the thin-film solar cell largely is classified into two types of transparent conductive layers; FTO (F doped SnO2 (fluorine-doped tin oxide)) and ZnO (zinc oxide).
A FTO transparent conductive layer is manufactured by atmospheric pressure CVD (Chemical Vapor Deposition) using HF and SnCl4 as reaction gases, and should have a relatively large thickness (normally ˜1 μm or more). Here, the deposition process is generally performed at a high temperature of 600° C. or above. The FTO transparent conductive layer is very weak against a hydrogen atmosphere, that is, the FTO transparent conductive layer has low transmittance due to a reduction reaction of hydrogen plasma that generates during PECVD (Plasma Enhanced Chemical Vapor Deposition) used to form an active layer (for example, amorphous Si) of a thin-film silicon solar cell.
On the other hand, the zinc oxide-based transparent conductive layer has excellent resistance against a reduction reaction of hydrogen plasma, and thus, its research is in active progress for the purpose of substituting for the FTO transparent conductive layer in a thin-film silicon solar cell. In the manufacture of the zinc oxide-based transparent conductive layer, atmospheric pressure CVD has problems with stability of an organic precursor and so on and does not yet have the established optimum conditions therefor, and sputtering has difficulty in surface texturing.
Accordingly, a two-step manufacturing method has been developed to manufacture a zinc oxide-based transparent conductive layer having a textured surface, which comprises depositing a thick zinc oxide-based transparent conductive layer with a sputter, and texturing the surface of the conductive layer through wet etching. However, this method needs wet etching after deposition of a thick layer, resulting in complicated process and increased time.